1. Field of the Invention
The present invention relates to a method and apparatus for detecting an abnormality (abnormal condition) in a rotation sensor, which detects an abnormal condition of a signal processing circuit related to a resolver. More particularly, the invention relates to a method and apparatus for detecting an abnormality in a rotation sensor, adapted to detect an abnormality in a resolver in a control circuit for driving a motor of an electric vehicle.
2. Description of Related Art
For example, at the occasion of controlling the number of rotations of a motor for driving an electric vehicle, it is necessary to accurately rotate the vector of a current supplied to the driving motor in accordance with the rotations of the driving motor. In an electric vehicle, therefore, it is necessary to accurately detect the rotor position (angle) of the driving motor of the electric vehicle. In fields, including the above kind of field, where the position of a rotor should be accurately detected, a resolver is used as means for detecting the position (angle) of the rotor.
Even if an apparatus using the resolver is employed as an angle detecting apparatus, however, when an abnormality occurs in an output of a signal processing circuit which obtains the angle of the rotor from an output of the resolver, the angle cannot be reliably accurately detected. In an apparatus disclosed in Japanese Patent Application Laid-Open No. 9-72758, an abnormality in the signal processing circuit can be detected. Since an A/D converting process is used for the abnormality detection and the angle is estimated from the result of the A/D conversion, however, the detection accuracy is low. The threshold of the abnormality detection has to be accordingly increased, so that it can be considered that the reliability of the abnormality detection deteriorates. Since the construction including the A/D converting circuit has the large number of components, the failure rate of the abnormality detecting circuit itself may be also increased.